Fuel-cell unit cell

ABSTRACT

Disclosed herein is a fuel-cell unit cell, at a first part of which: the fuel-cell unit cell has a bonding layer; between an outer peripheral edge portion of a first gas diffusion layer and a portion of a membrane-electrode assembly on an inner side from an outer peripheral edge portion thereof, the bonding layer bonds these portions together; between a first separator and the outer peripheral edge portion of the membrane-electrode assembly, the bonding layer is bonded to at least the outer peripheral edge portion of the membrane-electrode assembly; and between the first separator and a support frame and/or between a second separator and the support frame, the bonding layer bonds these parts together.

INCORPORATION BY REFERENCE

The disclosure of Japanese Patent Application No. 2019-179799 filed onSep. 30, 2019 including the specification, drawings and abstract isincorporated herein by reference in its entirety.

BACKGROUND 1. Technical Field

This disclosure relates to a fuel-cell unit cell.

2. Description of Related Art

In recent years, fuel cells that generate electricity by causing achemical reaction between an anode gas, such as hydrogen, and a cathodegas, such as oxygen, have become known.

Among known fuel-cell unit cells that are constituent elements of suchfuel cells, there are ones that have a configuration in which a gasdiffusion layer and a separator are disposed on each surface of amembrane-electrode assembly having an electrolyte membrane and electrodecatalyst layers respectively disposed on both surfaces of theelectrolyte membrane.

Japanese Patent No. 5681792 discloses a structure of a fuel-cell unitcell in which a resin frame member is provided so as to surround amembrane-electrode assembly, and this resin frame member is partiallyfused to a gas diffusion layer to fix the membrane-electrode assemblyand the resin frame member to each other.

Japanese Patent Application Publication No. 2016-162649 (JP 2016-162649A) discloses a structure of a fuel-cell unit cell in which amembrane-electrode assembly and a support frame are fixed to each otherby a bonding layer.

SUMMARY

The authors of this disclosure have found that the fuel-cell unit cellsdisclosed in Japanese Patent No. 5681792 and JP 2016-162649 A maydeteriorate as an internal structure of the fuel-cell unit cells, forexample, the membrane-electrode assembly tears and/or breaks duringmanufacturing of the fuel-cell unit cells, manufacturing of a fuel cellstack by stacking multiple fuel-cell unit cells, or usage of thefuel-cell unit cells, i.e., generation of electricity.

This problem is more specifically described as follows.

Gas diffusion layers used for fuel-cell unit cells are sometimes made ofan electrically conductive porous material, such as non-wovencarbon-fiber cloth. Some gas diffusion layers made of such a materialhave a rough end portion where, for example, carbon fibers are ruffled.

When such a gas diffusion layer is used, and the configuration in whicha gas diffusion layer is directly laid on a first surface of amembrane-electrode assembly except for an outer peripheral edge portionof the membrane-electrode assembly as disclosed in Japanese Patent No.5681792 and JP 2016-162649 A is adopted, the rough end portion of thegas diffusion layer, for example, the portion where carbon fibers areruffled may dig into and damage the membrane-electrode assembly, and mayfurther tear and/or break the membrane-electrode assembly, at a partwhere the end portion of the gas diffusion layer and themembrane-electrode assembly are in contact with each other.

If the membrane-electrode assembly gets damaged, the damaged portionbecomes fragile and may lead to tear and/or breakage of themembrane-electrode assembly. If the membrane-electrode assembly tearsand/or breaks, short-circuiting may occur inside the fuel-cell unitcell.

When the configuration in which there is a gap between a support frameand a gas diffusion layer as disclosed in JP 2016-162649 A is adopted,the portion of the fuel-cell unit cell where this gap is located, i.e.,the portion where the membrane-electrode assembly is exposed may deformin a thickness direction and fracture due to a gas pressure differencebetween a cathode side and an anode side during usage of the fuel-cellunit cell.

Thus, there is need for further enhancing the durability of fuel-cellunit cells.

An object of this disclosure is to provide a fuel-cell unit cell havinghigh mechanical durability.

The authors of this disclosure have found out the following solutionsthat can achieve this object:

First Aspect

A fuel-cell unit cell including:

(I) an electrode stack having

(a) a membrane-electrode assembly in which electrode catalyst layers arerespectively laid on both surfaces of an electrolyte layer,

(b) a first gas diffusion layer laid on a first surface of themembrane-electrode assembly except for an outer peripheral edge portionof the membrane-electrode assembly, and

(c) a second gas diffusion layer laid on a second surface of themembrane-electrode assembly;

(II) a support frame disposed so as to surround the first gas diffusionlayer;

(III) a first separator that is laid on a side of the electrode stack onwhich the first gas diffusion layer is located, in contact with thefirst gas diffusion layer, and that is fixed to the support frame; and

(IV) a second separator that is laid on a side of the electrode stack onwhich the second gas diffusion layer is located, in contact with thesecond gas diffusion layer, and that is fixed to the support frame,

wherein, at a first part of the fuel-cell unit cell:

the fuel-cell unit cell has a bonding layer;

between an outer peripheral edge portion of the first gas diffusionlayer and a portion of the membrane-electrode assembly on an inner sidefrom the outer peripheral edge portion of the membrane-electrodeassembly, the bonding layer bonds these portions together;

between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer is bonded to at least theouter peripheral edge portion of the membrane-electrode assembly; and

between the first separator and the support frame and/or between thesecond separator and the support frame, the bonding layer bonds theseparts together.

Second Aspect

In the fuel-cell unit cell according to the first aspect, the thicknessof the bonding layer between the first separator and the outerperipheral edge portion of the membrane-electrode assembly may be notsmaller than 50% of the distance between the first separator and theouter peripheral edge portion of the membrane-electrode assembly.

Third Aspect

In the fuel-cell unit cell according to the first or second aspect,between the first separator and the outer peripheral edge portion of themembrane-electrode assembly at the first part, the bonding layer maybond the first separator and the outer peripheral edge portion together.

Fourth Aspect

In the fuel-cell unit cell according to any one of the first to thirdaspects, between the second separator and the support frame at the firstpart, the bonding layer may bond these parts together.

Fifth Aspect

In the fuel-cell unit cell according to the fourth aspect, at a secondpart of the fuel-cell unit cell:

the second separator may have a reactant gas flow passage;

a cover plate may extend from between the second separator and thesecond gas diffusion layer to between the second separator and thesupport frame;

between the outer peripheral edge portion of the first gas diffusionlayer and the portion of the membrane-electrode assembly on the innerside from the outer peripheral edge portion of the membrane-electrodeassembly, the bonding layer may bond these portions together;

between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer may be bonded to theouter peripheral edge portion of the membrane-electrode assembly;

between the cover plate and the support frame, the bonding layer maybond these parts together; and

the bonding layer may be thus separated from the reactant gas flowpassage of the second separator.

Sixth Aspect

In the fuel-cell unit cell according to the fifth aspect, between thesecond separator and the support frame at the second part, the bondinglayer may bond also these parts together.

Seventh Aspect

In the fuel-cell unit cell according to the fifth or sixth aspect, at athird part of the fuel-cell unit cell:

the fuel-cell unit cell may have, between the second separator and thesupport frame, a communication passage that traverses the support frameso as to allow communication between the outside of the fuel-cell unitcell and the reactant gas flow passage;

the cover plate may extend from between the second separator and thesecond gas diffusion layer to between the second separator and thesupport frame;

between the outer peripheral edge portion of the first gas diffusionlayer and the portion of the membrane-electrode assembly on the innerside from the outer peripheral edge portion of the membrane-electrodeassembly, the bonding layer may bond these portions together;

between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer may be bonded to theouter peripheral edge portion of the membrane-electrode assembly;

between the cover plate and the support frame, the bonding layer maybond these parts together; and

the bonding layer may be thus separated from the communication passage.

According to this disclosure, a fuel-cell unit cell having highmechanical durability can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like numerals denotelike elements, and wherein:

FIG. 1 is a schematic view of a fuel-cell unit cell 100 as seen from theside of a first separator 30;

FIG. 2A is a sectional view of a fuel-cell unit cell 100 a according toa first embodiment of this disclosure, taken along a section similar tosection I-I′ of FIG. 1;

FIG. 2B is a sectional view of a fuel-cell unit cell 100 b according toa second embodiment of this disclosure, taken along section I-I′ similarto section I-I′ of FIG. 1;

FIG. 3A is a sectional view of a fuel-cell unit cell 100 c according toa third embodiment of this disclosure, taken along section I-I′ similarto section I-I′ of FIG. 1;

FIG. 3B is a sectional view of a fuel-cell unit cell 100 d according toa fourth embodiment of this disclosure, taken along section I-I′ similarto section I-I′ of FIG. 1;

FIG. 4 is a sectional view of a fuel-cell unit cell 100′ that is not anembodiment of this disclosure, taken along a section similar to sectionI-I′ of FIG. 1;

FIG. 5 is a schematic view of a fuel-cell unit cell 100 e according to afifth embodiment of this disclosure as seen from the side of the firstseparator 30;

FIG. 6 is a sectional view of the fuel-cell unit cell 100 e according tothe fifth embodiment of this disclosure, taken along section II-II′; and

FIG. 7 is a sectional view of the fuel-cell unit cell 100 e according tothe fifth embodiment of this disclosure, taken along a section similarto section III-III′ of FIG. 5.

DETAILED DESCRIPTION OF EMBODIMENTS

Embodiments of this disclosure will be described in detail below. Thisdisclosure is not limited to the following embodiments but can beimplemented with various changes made thereto within the scope of thegist of the disclosure.

A fuel-cell unit cell of this disclosure includes:

(I) an electrode stack having

(a) a membrane-electrode assembly in which electrode catalyst layers arerespectively laid on both surfaces of an electrolyte layer,

(b) a first gas diffusion layer laid on a first surface of themembrane-electrode assembly except for an outer peripheral edge portionof the membrane-electrode assembly, and

(c) a second gas diffusion layer laid on a second surface of themembrane-electrode assembly;

(II) a support frame disposed so as to surround the first gas diffusionlayer;

(III) a first separator that is laid on a side of the electrode stack onwhich the first gas diffusion layer is located, in contact with thefirst gas diffusion layer, and that is fixed to the support frame; and

(IV) a second separator that is laid on a side of the electrode stack onwhich the second gas diffusion layer is located, in contact with thesecond gas diffusion layer, and that is fixed to the support frame.

At a first part of the fuel-cell unit cell of this disclosure: thefuel-cell unit cell has a bonding layer; between an outer peripheraledge portion of the first gas diffusion layer and a portion of themembrane-electrode assembly on an inner side from the outer peripheraledge portion thereof, the bonding layer bonds these portions together;between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer is bonded to at least theouter peripheral edge portion of the membrane-electrode assembly; andbetween the first separator and the support frame and/or between thesecond separator and the support frame, the bonding layer bonds theseparts together.

The portion of the membrane-electrode assembly on the inner side fromthe outer peripheral edge portion thereof means a portion on the innerside from the outer peripheral edge portion in an in-plane direction ofthe membrane-electrode assembly.

First Part

At the first part of the fuel-cell unit cell of this disclosure: thefuel-cell unit cell has the bonding layer; between the outer peripheraledge portion of the first gas diffusion layer and the portion of themembrane-electrode assembly on the inner side from the outer peripheraledge portion thereof, the bonding layer bonds these portions together;between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer is bonded to at least theouter peripheral edge portion of the membrane-electrode assembly; andbetween the first separator and the support frame and/or between thesecond separator and the support frame, the bonding layer bonds theseparts together.

The principle underlying the high mechanical durability of the fuel-cellunit cell of this disclosure is, without it limiting the disclosure, asfollows:

The first part of fuel-cell unit cell of this disclosure has theabove-described configuration in which the bonding layer is interposedbetween an end portion of the gas diffusion layer and themembrane-electrode assembly. Thus, even when the gas diffusion layer hasa rough end portion, for example, even when the gas diffusion layer madeof an electrically conductive porous material, such as non-wovencarbon-fiber cloth, has an end portion where carbon fibers are ruffled,this end portion of the gas diffusion layer and the membrane-electrodeassembly do not directly come into contact with each other. It istherefore less likely that the rough end portion of the gas diffusionlayer, for example, the portion where carbon fibers are ruffled may tearand/or break the membrane-electrode assembly by digging into themembrane-electrode assembly or damaging and further making a hole in themembrane-electrode assembly.

Between the first separator and the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer is bonded to the outerperipheral edge portion of the membrane-electrode assembly, i.e., theportion of the membrane-electrode assembly that is exposed through a gapbetween the support frame and the first gas diffusion layer. Thus, thisportion is reinforced by the bonding layer, so that themembrane-electrode assembly is less likely to deform due to a gaspressure difference between a cathode side and an anode side.

For these reasons, the fuel-cell unit cell of this disclosure has highmechanical durability.

This principle will be more specifically described using examples offuel-cell unit cells according to embodiments of this disclosure and afuel-cell unit cell that is not an embodiment of this disclosure.

FIG. 1 is a schematic view of a fuel-cell unit cell 100 as seen from theside of a first separator 30. In FIG. 1, L and W represent alongitudinal direction of the fuel-cell unit cell and a width directionof the fuel-cell unit cell, respectively.

As shown in FIG. 1, the fuel-cell unit cell 100 has, on the side of thefirst separator 30, first gas pass-through openings 10 a, 10 f, coolantpass-through openings 10 b, 10 e, and second gas pass-through openings10 c, 10 d.

FIG. 2A is a sectional view of a fuel-cell unit cell 100 a according toa first embodiment of this disclosure, taken along section I-I′. In FIG.2A, W and T represent a width direction of the fuel-cell unit cell and athickness direction, i.e., a stacking direction of the fuel-cell unitcell, respectively.

As shown in FIG. 2A, the fuel-cell unit cell 100 a according to thefirst embodiment of this disclosure has an electrode stack 20. Theelectrode stack 20 has: a membrane-electrode assembly 21 in whichelectrode catalyst layers 21 q, 21 r are respectively laid on bothsurfaces of an electrolyte layer 21 p; a first gas diffusion layer 22laid on a first surface of the membrane-electrode assembly 21 except foran outer peripheral edge portion 21 a of the membrane-electrode assembly21; and a second gas diffusion layer 23 laid on a second surface of themembrane-electrode assembly 21.

The fuel-cell unit cell 100 a according to the first embodiment of thisdisclosure further has: a support frame 50 disposed so as to surroundthe first gas diffusion layer 22; the first separator 30 that is laid ona side of the electrode stack 20 on which the first gas diffusion layer22 is located, in contact with the first gas diffusion layer 22, andthat is fixed to the support frame 50; and a second separator 40 that islaid on a side of the electrode stack 20 on which the second gasdiffusion layer 23 is located, in contact with the second gas diffusionlayer 23, and that is fixed to the support frame 50.

The first separator 30 and the second separator 40 have reactant gasflow passages 31, 41, respectively.

In FIG. 2A, the support frame 50 is disposed so as to surround the firstgas diffusion layer 22 and the electrode stack 20. However, the supportframe 50 should be disposed so as to surround at least the first gasdiffusion layer 22. For example, as in a fuel-cell unit cell 100 baccording to a second embodiment of this disclosure shown in FIG. 2B,the support frame 50 may be disposed so as to overlap themembrane-electrode assembly 21 in the thickness direction T of thefuel-cell unit cell 100 b.

At a first part of the fuel-cell unit cell 100 a: the fuel-cell unitcell 100 a has a bonding layer 60; between an outer peripheral edgeportion 22 a of the first gas diffusion layer 22 and a portion of themembrane-electrode assembly 21 on an inner side from the outerperipheral edge portion 21 a, the bonding layer 60 bonds these portionstogether; between the first separator 30 and the outer peripheral edgeportion 21 a of the membrane-electrode assembly 21, the bonding layer 60is bonded to at least the outer peripheral edge portion 21 a of themembrane-electrode assembly 21; and between the first separator 30 andthe support frame 50 and/or between the second separator 40 and thesupport frame 50, the bonding layer 60 bonds these parts together. Thesupport frame 50 is bonded to the first separator 30 and the secondseparator 40 by separate bonding layers 70, although this configurationis not essential for the fuel-cell unit cell of this disclosure.

Thus, the bonding layer 60 is interposed between an end portion of thefirst gas diffusion layer 22 and the membrane-electrode assembly 21, sothat the end portion of the first gas diffusion layer 22 and themembrane-electrode assembly 21 do not directly come into contact witheach other. Therefore, even when the first gas diffusion layer 22 has arough end portion, the membrane-electrode assembly 21 is less likely toget damaged.

Between the first separator 30 and the outer peripheral edge portion 21a of the membrane-electrode assembly 21, the bonding layer 60 is bondedto the outer peripheral edge portion 21 a of the membrane-electrodeassembly 21. Thus, this portion is reinforced by the bonding layer 60,so that the membrane-electrode assembly 21 is less likely to deform dueto a gas pressure difference between the cathode side and the anodeside.

Further, an end portion of the support frame 50 facing the first gasdiffusion layer 22 is fixed by the first separator 30. Thus, even whenthe support frame 50 deforms by expanding or contracting due to heatresulting from using the fuel-cell unit cell 100 a, i.e., generatingelectricity, the relationship between the relative positions of thesupport frame 50 and the membrane-electrode assembly 21 is less likelyto change. Therefore, the mechanical durability of the fuel-cell unitcell 100 a, especially that during usage of the fuel-cell unit cell, canbe further enhanced.

Between the second separator 40 and the support frame 50, the bondinglayer 60 may bond these parts together, as in a fuel-cell unit cell 100c according to a third embodiment of this disclosure shown in FIG. 3Aand a fuel-cell unit cell 100 d according to a fourth embodiment of thisdisclosure shown in FIG. 3B.

By contrast, for example, in a fuel-cell unit cell 100′ as shown in FIG.4 that is not an embodiment of this disclosure, the end portion of thefirst gas diffusion layer 22 and the membrane-electrode assembly 21 aredirectly in contact with each other. Thus, the rough end portion of thefirst gas diffusion layer 22 may damage and further make a hole in themembrane-electrode assembly 21, at the part where the end portion of thefirst gas diffusion layer 22 and the membrane-electrode assembly 21 arein contact with each other.

Moreover, there is a portion between the first separator 30 and theouter peripheral edge portion 21 a of the membrane-electrode assembly 21where the bonding layer 60 is not bonded to the outer peripheral edgeportion 21 a of the membrane-electrode assembly 21, so that themembrane-electrode assembly 21 is likely to deform and get damaged atthis portion due to a gas pressure difference between the cathode sideand the anode side during usage of the fuel-cell unit cell.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly at thefirst part is preferably not smaller than 50% of the distance betweenthe first separator and the outer peripheral edge portion of themembrane-electrode assembly. Thus, the outer peripheral edge portion ofthe membrane-electrode assembly is further reinforced, so that themembrane-electrode assembly is even less likely to deform due to a gaspressure difference between the cathode side and the anode side duringusage of the fuel-cell unit cell.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly may benot smaller than 50%, 60%, 70%, or 80% of the distance between the firstseparator and the outer peripheral edge portion of themembrane-electrode assembly. The thickness of the bonding layer is morepreferably 100% of the distance, which means that the bonding layerbetween the first separator and the outer peripheral edge portion of themembrane-electrode assembly bonds the first separator and the outerperipheral edge portion together.

Second Part

When the bonding layer between the second separator and the supportframe bonds these parts together at the first part of the fuel-cell unitcell of this disclosure, at a second part of the fuel-cell unit cell:the second separator may have a reactant gas flow passage; a cover platemay extend from between the second separator and the second gasdiffusion layer to between the second separator and the support frame;between the outer peripheral edge portion of the first gas diffusionlayer and the portion of the membrane-electrode assembly on the innerside from the outer peripheral edge portion thereof, the bonding layermay bond these portions together; between the first separator and theouter peripheral edge portion of the membrane-electrode assembly, thebonding layer may be bonded to the outer peripheral edge portion of themembrane-electrode assembly; between the cover plate and the supportframe, the bonding layer may bond these parts together; and the bondinglayer may be thus separated from the reactant gas flow passage of thesecond separator.

Here, the reactant gas flow passage is a flow passage that is used tosupply a reactant gas, supplied from the outside of the fuel-cell unitcell, to the gas diffusion layer of the fuel-cell unit cell, and todischarge a reactant gas that has not been consumed in cell reactions tothe outside of the fuel-cell unit cell. Examples of the reactant gasinclude an anode gas, such as a hydrogen gas, and a cathode gas, such asan oxygen gas.

When the second part of the fuel-cell unit cell of this disclosure hasthe above-described configuration in which the cover plate extends frombetween the second separator and the second gas diffusion layer tobetween the second separator and the support frame, the bonding layer isseparated from the reactant gas flow passage of the second separator, sothat the bonding layer while being formed is less likely to penetrateinto and close the reactant gas flow passage. Moreover, as highmechanical durability as at the first part can be achieved at the secondpart.

At the second part of the fuel-cell unit cell of this disclosure, thebonding layer between the second separator and the support frame mayalso bond these parts together.

Since the cover plate and the second separator are thus bonded togetherthrough the bonding layer, even when, for example, stress is applied tothe fuel-cell unit cell from the outside and the fuel-cell unit cellwarps in an in-plane direction, the positional relationship between thecover plate and the second separator is less likely to change.Therefore, the strength of the second part of the fuel-cell unit cellcan be further enhanced.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly at thesecond part is preferably not smaller than 50% of the distance betweenthe first separator and the outer peripheral edge portion of themembrane-electrode assembly. Thus, the outer peripheral edge portion ofthe membrane-electrode assembly is further reinforced, so that themembrane-electrode assembly is even less likely to deform due to a gaspressure difference between the cathode side and the anode side duringusage of the fuel-cell unit cell.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly may benot smaller than 50%, 60%, 70%, or 80% of the distance between the firstseparator and the outer peripheral edge portion of themembrane-electrode assembly. The thickness of the bonding layer is morepreferably 100% of the distance, which means that the bonding layerbetween the first separator and the outer peripheral edge portion of themembrane-electrode assembly bonds the first separator and the outerperipheral edge portion together.

The position of the second part in the fuel-cell unit cell of thisdisclosure is not particularly limited. For example, the second part canbe disposed in an area adjacent to the first gas pass-through openings10 a, 10 f, the coolant pass-through openings 10 b, 10 e, or the secondgas pass-through openings 10 c, 10 d, like the area where section II-II′of FIG. 5 is located.

Specifically, the second part may have the configuration as shown inFIG. 6.

FIG. 6 is a sectional view of a fuel-cell unit cell 100 e according to afifth embodiment of this disclosure, taken along section II-II′.

As shown in FIG. 6, at the second part of the fuel-cell unit cell 100 eaccording to the fifth embodiment of this disclosure: the secondseparator 40 may have the reactant gas flow passages 41; a cover plate80 may extend from between the second separator 40 and the second gasdiffusion layer 23 to between the second separator 40 and the supportframe 50; between the outer peripheral edge portion 22 a of the firstgas diffusion layer 22 and the portion of the membrane-electrodeassembly 21 on the inner side from the outer peripheral edge portion 21a, the bonding layer 60 may bond these portions together; between thefirst separator 30 and the outer peripheral edge portion 21 a of themembrane-electrode assembly 21, the bonding layer 60 may be bonded tothe outer peripheral edge portion 21 a of the membrane-electrodeassembly 21; between the cover plate 80 and the support frame 50, thebonding layer 60 may bond these parts together; and the bonding layer 60may be thus separated from the reactant gas flow passages 41 of thesecond separator 40.

Third Part

When the second part of the fuel-cell unit cell of this disclosure hasthe above-described configuration, at a third part of the fuel-cell unitcell: the fuel-cell unit cell may have, between the second separator andthe support frame, a communication passage that traverses the supportframe so as to allow communication between the outside of the fuel-cellunit cell and the reactant gas flow passage; a cover plate may extendfrom between the second separator and the second gas diffusion layer tobetween the second separator and the support frame; between the outerperipheral edge portion of the first gas diffusion layer and the portionof the membrane-electrode assembly on the inner side from the outerperipheral edge portion, the bonding layer may bond these portionstogether; between the first separator and the outer peripheral edgeportion of the membrane-electrode assembly, the bonding layer may bebonded to the outer peripheral edge portion of the membrane-electrodeassembly; between the cover plate and the support frame, the bondinglayer may bond these parts together; and the bonding layer may be thusseparated from the communication passage.

Here, the communication passage is a passage that traverses the supportframe so as to allow communication between the outside of the fuel-cellunit cell and the reactant gas flow passage. The communication passageis a passage through which the reactant gas flows in and out between theoutside and inside of the fuel-cell unit cell. Examples of the reactantgas include an anode gas, such as a hydrogen gas, and a cathode gas,such as an oxygen gas.

When the third part of the fuel-cell unit cell of this disclosure hasthe above-described configuration in which the communication passage isformed between the second separator and the support frame and thebonding layer is separated from the communication passage at the thirdpart, the bonding layer is less likely to close the communicationpassage. Moreover, as high mechanical durability as at the first partcan be achieved at the third part.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly at thethird part is preferably not smaller than 50% of the distance betweenthe first separator and the outer peripheral edge portion of themembrane-electrode assembly. Thus, the outer peripheral edge portion ofthe membrane-electrode assembly is further reinforced, so that themembrane-electrode assembly is even less likely to deform due to a gaspressure difference between the cathode side and the anode side duringusage of the fuel-cell unit cell.

The thickness of the bonding layer between the first separator and theouter peripheral edge portion of the membrane-electrode assembly may benot smaller than 50%, 60%, 70%, or 80% of the distance between the firstseparator and the outer peripheral edge portion of themembrane-electrode assembly. The thickness of the bonding layer is morepreferably 100% of the distance, which means that the bonding layerbetween the first separator and the outer peripheral edge portion of themembrane-electrode assembly bonds the first separator and the outerperipheral edge portion together.

The position of the third part in the fuel-cell unit cell of thisdisclosure is not particularly limited. For example, the third part canbe disposed in an area where the first gas pass-through openings 10 a,10 f, the coolant pass-through openings 10 b, 10 e, or the second gaspass-through openings 10 c, 10 d are disposed, like the area wheresection III-III′ of FIG. 5 is located.

When the second part of the fuel-cell unit cell of this disclosure has,for example, the structure as shown in FIG. 6, the third part thereofmay have, for example, the structure as shown in FIG. 7.

FIG. 7 is a sectional view of the fuel-cell unit cell 100 e according tothe fifth embodiment of this disclosure, taken along section III-III′.

As shown in FIG. 7, the fuel-cell unit cell 100 e of this disclosurehas, between the second separator 40 and the support frame 50, acommunication passage 90 that traverses the support frame 50 so as toallow communication between the outside of the fuel-cell unit cell 100 eand the reactant gas flow passage 41. The cover plate 80 extends frombetween the second separator 40 and the second gas diffusion layer 23 tobetween the second separator 40 and the support frame 50. Between theouter peripheral edge portion 22 a of the first gas diffusion layer 22and the portion of the membrane-electrode assembly 21 on the inner sidefrom the outer peripheral edge portion 21 a, the bonding layer 60 bondsthese portions together. Between the first separator 30 and the outerperipheral edge portion 21 a of the membrane-electrode assembly 21, thebonding layer 60 is bonded to the outer peripheral edge portion 21 a ofthe membrane-electrode assembly 21. Between the cover plate 80 and thesupport frame 50, the bonding layer 60 bonds these parts together. Thebonding layer 60 is thus separated from the communication passage 90.

Electrode Stack

In this disclosure, the electrode stack has the following (a) to (c):

(a) a membrane-electrode assembly in which electrode catalyst layers arerespectively laid on both surfaces of an electrolyte layer;

(b) a first gas diffusion layer laid on a first surface of themembrane-electrode assembly except for an outer peripheral edge portionof the membrane-electrode assembly; and

(c) a second gas diffusion layer laid on a second surface of themembrane-electrode assembly.

Membrane-Electrode Assembly

The membrane-electrode assembly has the electrolyte layer and theelectrode catalyst layers respectively laid on both surfaces of theelectrolyte layer.

Electrolyte Layer

An arbitrary material that can be used for an electrolyte layer of afuel-cell unit cell can be used as the material of the electrolytelayer. Examples of such a material include fluorine polymer membraneshaving ion conductivity, more specifically, ion-exchange membraneshaving proton conductivity and containing perfluorosulfonic acid.

Electrode Catalyst Layer

Examples of the electrode catalyst layer include an anode catalyst layerand a cathode catalyst layer. The anode catalyst layer and the cathodecatalyst layer may be catalyst layers in which a catalytic metal issupported by a carrier.

The catalytic metal may be an arbitrary catalytic metal that is used fora fuel cell catalyst. Examples of such a catalytic metal include Pt, Pd,Rh, and alloys containing these metals.

The carrier may be an arbitrary carrier that is used for a fuel cellcatalyst. Examples of such a carrier include carbon carriers, morespecifically, carbon particles of glassy carbon, carbon black, activecarbon, coke, natural graphite, artificial graphite, or the like.

Gas Diffusion Layer

In this disclosure, the first gas diffusion layer is laid on the firstsurface of the membrane-electrode assembly except for the outerperipheral edge portion thereof, and the second gas diffusion layer islaid on the second surface of the membrane-electrode assembly.

Of the first gas diffusion layer and the second gas diffusion layer, oneis an anode gas diffusion layer and the other is a cathode gas diffusionlayer.

The material of the first gas diffusion layer and the second gasdiffusion layer may be an arbitrary material that can be used for ananode gas diffusion layer and a cathode gas diffusion layer of a fuelcell catalyst. Examples of such a material include electricallyconductive porous materials. More specifically, examples of such porousmaterials include porous carbon materials, such as carbon paper, carboncloth, and glasslike carbon, and porous metal materials, such as metalmesh and foam metal.

Support Frame

The support frame is disposed so as to surround the first gas diffusionlayer.

When the fuel-cell unit cell of this disclosure has the third part, thesupport frame may have, at the third part, a groove that allowscommunication between the inside and outside of the fuel-cell unit cell,and the communication passage may be formed by this groove.

The support frame is made of an arbitrary material that can provideelectrical insulation and airtightness. Examples of such a materialinclude crystalline polymers, more specifically, engineering plastics.Examples of engineering plastics include polyethylene naphthalate (PEN)resins and polyethylene terephthalate (PET) resins.

First Separator

The first separator is laid on a side of the electrode stack on whichthe first gas diffusion layer is located, in contact with the first gasdiffusion layer, and is fixed to the support frame.

The first separator may have a plurality of grooves in a surface facingthe first gas diffusion layer, and the reactant gas flow passages may beformed by these grooves. The grooves may have an arbitrary shape, forexample, a serpentine shape, as long as the grooves can supply thereactant gas to the first gas diffusion layer.

The first separator may have a first gas pass-through opening, a coolantpass-through opening, and a second gas pass-through opening.

The material of the first separator may be an arbitrary material thatcan be used for a separator of a fuel-cell unit cell, and may be amaterial having gas impermeability and electrical conductivity. Examplesof such a material include dense carbon formed by compressing carbon soas to have gas impermeability, and metal plates formed by pressing.

Second Separator

The second separator is laid on a side of the electrode stack on whichthe second gas diffusion layer is located, in contact with the secondgas diffusion layer, and is fixed to the support frame.

The material and structure of the second separator may be the same asthose of the first separator.

Bonding Layer

As the bonding layer, a layer of an arbitrary adhesive can be used thatcan bond together the first separator, the first gas diffusion layer,the membrane-electrode assembly, the support frame, and the secondseparator, and that can keep these members bonded together under theservice conditions of the fuel-cell unit cell.

Examples of such an adhesive include, but are not limited to, adhesiveresins such as thermoplastic resins, thermosetting resins, and UV-curingresins. When a thermoplastic resin is used as the adhesive, that resinpreferably has a softening point higher than the temperature of heatgenerated during usage of the fuel-cell unit cell.

Cover Plate

The material of the cover plate is not particularly limited as long asit is a sheet-shaped material that can be bonded to the first gasdiffusion layer, the membrane-electrode assembly, and the support frameby the bonding layer. Examples of such a material include titanium,stainless steel, polyphenylene sulfide (PPS), and polypropylene (PP).

None of the drawings used to describe this disclosure is intended tolimit the configuration, structure, and other features of the fuel-cellunit cell of this disclosure.

What is claimed is:
 1. A fuel-cell unit cell comprising: (I) anelectrode stack having (a) a membrane-electrode assembly in whichelectrode catalyst layers are respectively laid on both surfaces of anelectrolyte layer, (b) a first gas diffusion layer laid on a firstsurface of the membrane-electrode assembly except for an outerperipheral edge portion of the membrane-electrode assembly, and (c) asecond gas diffusion layer laid on a second surface of themembrane-electrode assembly; (II) a support frame disposed so as tosurround the first gas diffusion layer; (III) a first separator that islaid on a side of the electrode stack on which the first gas diffusionlayer is located, in contact with the first gas diffusion layer, andthat is fixed to the support frame; and (IV) a second separator that islaid on a side of the electrode stack on which the second gas diffusionlayer is located, in contact with the second gas diffusion layer, andthat is fixed to the support frame, wherein a first part of thefuel-cell unit cell comprises a bonding layer; between an outerperipheral edge portion of the first gas diffusion layer and a portionof the membrane-electrode assembly on an inner side from the outerperipheral edge portion of the membrane-electrode assembly, the bondinglayer bonds these portions together; between the first separator and theouter peripheral edge portion of the membrane-electrode assembly, thebonding layer is bonded to at least the outer peripheral edge portion ofthe membrane-electrode assembly; and between the first separator and thesupport frame and/or between the second separator and the support frame,the bonding layer bonds these parts together.
 2. The fuel-cell unit cellaccording to claim 1, wherein a thickness of the bonding layer betweenthe first separator and the outer peripheral edge portion of themembrane-electrode assembly is not smaller than 50% of a distancebetween the first separator and the outer peripheral edge portion of themembrane-electrode assembly.
 3. The fuel-cell unit cell according toclaim 1, wherein, between the first separator and the outer peripheraledge portion of the membrane-electrode assembly at the first part, thebonding layer bonds the first separator and the outer peripheral edgeportion together.
 4. The fuel-cell unit cell according to claim 1,wherein, between the second separator and the support frame at the firstpart, the bonding layer bonds these parts together.
 5. The fuel-cellunit cell according to claim 4, wherein, at a second part of thefuel-cell unit cell, the second separator has a reactant gas flowpassage; a cover plate extends from between the second separator and thesecond gas diffusion layer to between the second separator and thesupport frame; between the outer peripheral edge portion of the firstgas diffusion layer and the portion of the membrane-electrode assemblyon the inner side from the outer peripheral edge portion of themembrane-electrode assembly, the bonding layer bonds these portionstogether; between the first separator and the outer peripheral edgeportion of the membrane-electrode assembly, the bonding layer is bondedto the outer peripheral edge portion of the membrane-electrode assembly;and between the cover plate and the support frame, the bonding layerbonds these parts together; and the bonding layer is thus separated fromthe reactant gas flow passage of the second separator.
 6. The fuel-cellunit cell according to claim 5, wherein, between the second separatorand the support frame at the second part, the bonding layer bonds alsothese parts together.
 7. The fuel-cell unit cell according to claim 5,wherein, at a third part of the fuel-cell unit cell, the fuel-cell unitcell has, between the second separator and the support frame, acommunication passage that traverses the support frame so as to allowcommunication between an outside of the fuel-cell unit cell and thereactant gas flow passage; the cover plate extends from between thesecond separator and the second gas diffusion layer to between thesecond separator and the support frame; between the outer peripheraledge portion of the first gas diffusion layer and the portion of themembrane-electrode assembly on the inner side from the outer peripheraledge portion of the membrane-electrode assembly, the bonding layer bondsthese portions together; between the first separator and the outerperipheral edge portion of the membrane-electrode assembly, the bondinglayer is bonded to the outer peripheral edge portion of themembrane-electrode assembly; between the cover plate and the supportframe, the bonding layer bonds these parts together; and the bondinglayer is thus separated from the communication passage.